1. Field of the Invention
The present invention relates to an apparatus for automatically locking and unlocking doors of a vehicle based on mutual communication between a portable unit carried by a driver of the vehicle (a portable unit user) and a controller built-in the vehicle. More particularly, the present invention relates to an automatic vehicle door locking/unlocking apparatus for automatically locking the doors of the vehicle even when the portable unit user is not in an effective communication range of the portable unit, i.e., the portable unit user is too far away from the vehicle. An example of the above situation may be that after all passengers get off the vehicle, and the doors are closed and locked, but the portable unit user unlocks the doors for one of the passengers who needs to fetch something left inside the vehicle. Afterward, the passenger closes the door, and the locking of the door is accomplished even if the portable unit user is not in the effective communication range.
2. Description of the Related Art
Recently, apparatus for remotely locking and unlocking doors of a vehicle with a portable unit that is capable of sending and receiving a radio signal have been in widely used.
For example, Japanese patent publication No. 3-55633 discloses a vehicle lock control apparatus which allows a controller built-in a vehicle and a portable unit to communicate with each other when an activating switch mounted on the outer surface of a driver-side door is operated, and which locks or unlocks the doors of the vehicle if a legitimate portable unit is present near the vehicle. As shown in FIGS. 9 and 10 of the publication, the disclosed vehicle lock control apparatus has a door opening/closing detecting means for preventing the vehicle from being unattended with unlocked doors due to malfunctioning of the activating switch or forgetting of the locking operation. Specifically, after confirming that the portable unit was near the driver-side door (near the vehicle) when the doors were opened or closed, the doors are automatically locked after a predetermined period of time has lapsed if the portable unit is not near the vehicle.
Japanese laid-open patent publication No. 2001-145017 discloses, as shown in FIGS. 6 through 9 of the publication, an apparatus for automatically locking the doors of a vehicle reliably when a portable unit user is positioned out of the communication range of the portable unit at the time the doors are closed and a door controller on the vehicle and the portable unit fail to communicate with each other, such as when the driver who is carrying the portable unit gets off the vehicle and quickly leaves the vehicle forcibly closing the door. The disclosed apparatus detects whether or not the portable unit is present in the passenger's compartment or in a predetermined range near the driver-side door when the driver-side door is opened and closed, and automatically locks the doors in various manners including the generation of a warning, based on the detected results in both the passenger's compartment and the predetermined range.
According to the conventional apparatus referred to above, the controller and the portable unit communicate with each other when the doors are opened and/or closed, and the doors are automatically locked based on the results of the communications. If the portable unit user or a passenger has forgotten something in the vehicle whose doors are locked, then when the portable unit user unlocks the doors with the activating switch and walks out of the communication range, and thereafter the portable unit user or the passenger opens and closes the assistant-side door or the door therebehind where no antenna is installed, the doors are not automatically locked, or the doors are automatically locked but a warning may be produced or not depending on the position of the portable unit user when the passenger closes and opens the door. Therefore, the automatic door locking function of the conventional apparatus is low in reliability or operationally limited.